The present invention relates to a die set for press-forming an article from sheet material, and particularly to a system for breaking any vacuum created between the die set and the article during press-forming of the sheet material to aid in releasing the article from the die set.
Press-formed articles are often damaged during manufacture as a result of article-sticking problems that arise during operation of the die press. Sheet material that has been press-formed under high pressure to produce an article has a tendency to stick to the male and/or female die due to creation of a vacuum between such die(s) and the sheet material during press-forming of the article. Damage to the article or other disruption to the press cycle can occur during release of the article from the press as a result of such a vacuum-induced sticking problem.
It has been observed that the foregoing sticking problem occurs frequently when articles are formed in a thermal press from blanks comprising polymer-impregnated paper sheet material. At predetermined high pressures and temperatures, the heated polymeric material impregnated in the paper sheet material is activated to flow and consolidate the substantially paper article. Such a conversion causes the finish-formed article to look and feel like plastic even though it is mostly paper and other non-plastic ingredients. Before it is pressed, the polymer-impregnated material has a rough porous surface. After pressing, the material has a less porous surface resulting in a smooth, plastic feel preferred by many consumers. Formation of such a smooth surface against the male and/or female die during operation of the thermal press increases the likelihood that a vacuum will be created between the surface and said die(s), thereby resulting in sticking problems associated with a vacuum at the interface between a die and a press-formed article in the die.
One object of the present invention is to provide means for breaking vacuums created during press-forming of an article in a die press at one or more selected stages of each press cycle to aid in dislodging a press-formed article upon separation of mating male and female dies and preparatory to ejection of the article from the die press.
Another object of the present invention is to provide improved means for separating trim waste from a pre-formed sheet material article.
In accordance with the present invention, an improved die set is provided for forming an article from sheet material. The die set includes male die means, female die means, and press means for providing relative movement between the male and female die means to press sheet material positioned therebetween, thereby forming the article. Dislodging means is provided for selectively injecting air between the press-formed sheet material and at least one of the male and female die means during separation of the male and female die means. When activated, the dislodging means acts to break any vacuum formed, as the sheet material is pressed, between said press-formed sheet material and said at least one of the male and female die means.
In preferred embodiments, the dislodging means is set up to break a vacuum created between the sheet material and the male die means and further includes first air supply means associated with the male die means. Desirably, the male die means includes a male mold element, clamp means adjacent the male mold element for selectively holding the sheet material against the female die means during separation of the male mold element and the female die means, and means for providing relative movement between the clamp means and the male mold element to permit movement of the male mold element relative to the female die means.
The clamp means and the male mold element cooperate to define a passageway therebetween interconnecting the first air supply means and the press-formed sheet material during separation of the clamp means and the male mold element. Provision of this passageway permits air from the first air supply means to be injected between the male die means and the press-formed sheet material. Advantageously, this injected air aids in breaking any vacuum which may have been created between the male mold element and the press-formed sheet material during formation of the article in the die set.
The male die means further includes retraction means for moving the clamp means away from the female die means. The first air supply means desirably includes a source of compressed air having a pressure selected to exert a substantially predetermined force on the press-formed sheet material. Advantageously, the compressed air acts to hold the sheet material against the female die means during movement of the clamp means away from the female die means. Furthermore, the passageway provided in between the clamp means and the male mold element communicates with an interface between the clamp means and the press-formed sheet material. This arrangement advantageously permits compressed air from the first air supply means to be injected between the clamp means and the press-formed sheet material to break any vacuum formed therebetween while the compressed air continues to exert a downward force on the sheet material in the female die means.
Also in preferred embodiments, the dislodging means is set up to break a vacuum created between the sheet material and the female die means and further includes second air supply means associated with the female die means. Desirably, the female die means includes a female mold element and ejector means for ejecting an article formed in the female mold element, and means for providing relative movement between the ejector means and the female mold element. The female mold element and the ejector means cooperate to define a passageway therebetween interconnecting the second air supply means and the press-formed sheet material during separation of the female mold element and the ejector means. Provision of this passageway permits air from the second air supply means to be injected between the female die means and the press-formed sheet material to aid in breaking any vacuum created therebetween.
The improved die set further includes trim means for separating the press-formed sheet material into the article and excess trim waste so as to define a peripheral edge of the article and discharge means for selectively moving the excess trim waste away from the female die means. Illustratively, the discharge means includes an air nozzle for blowing either the excess trim waste or the article away from the female die means and a deflector for selectively routing the excess trim waste toward a scrap collector and the article in another direction toward an article collector.
Also in accordance with the present invention an improved method is provided of releasing sheet material press-formed in a die assembly between mating male and female die means from the die assembly. Illustratively, the method includes the steps of initially injecting air between the male die means and sheet material in the die assembly to break any vacuum created between the male die means and said sheet material during press-forming of the sheet material, and subsequently injecting air between the female die means and sheet material in the die assembly to break any vacuum created between the female die means and said sheet material during press-forming of the sheet material. In preferred embodiments, the method further includes the steps of cutting the press-formed sheet material to provide an article, withdrawing the male die means from mating engagement with the female die means after the sheet material is press-formed while injecting air between the male die means and the press-formed sheet material, and subsequently ejecting the article from the female die means while injecting air between the female die means and the press-formed sheet material.
Also, in preferred embodiments, the method further includes the steps of clamping the sheet material against the female die means during the initial injecting step using a clamp that is movably supported in the male die means, separating the male die means and the clamp to define a space therebetween communicating with an interface between the male die means and the sheet material for receiving initially injected air, providing a source of compressed air having a predetermined pressure, and using the compressed air to accomplish the initial air-injecting step so that a pneumatic-biasing force corresponding to the pressure of the compressed air is exerted on the clamped sheet material, thereby aiding in holding the sheet material against the female die means. The clamp and the male die means desirably cooperate to define a molding surface for engaging the sheet material and pressing the sheet material into the female die means.
Subsequently, the clamp is moved away from the female die means. The predetermined pressure is selected to retain the pneumatically-biased sheet material in clamped position during such movement of the clamp. Advantageously, the compressed air penetrates an interface between the clamp and the sheet material to break any vacuum created therebetween during forming of the sheet material.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.